Transistor amplifiers which are often adopted in electronic devices reach their peak efficiency under specific input power. This power is related to the structure (circuit parts and layout), load condition and supply voltage. A typical electronic device, such as a radio frequency power amplifier (PA), is generally designed to achieve its optimal performance under the peak input signal. Because the dynamic bandwidth of the input signal of a PA is large, the input signal reaches the peak only occasionally so that the efficiency of a transistor linear PA is normally low.
A common solution for increasing the efficiency of a PA is based on the power supply with such techniques as Traffic Tracking (TT), Envelop Tracking (ET) and Envelope Elimination and Restoration (EER), where the drain supply voltage of the PA is dynamically changed according to the work requirements of the PA so as to increase the average system efficiency. In other similar scenarios, a power supply based solution may also be needed to improve the work efficiency of a system.
To implement the above power supply based solution, a Pulse Width Modulation (PWM) based method is adopted in the prior art so as to achieve an efficient voltage variable power supply.
In the prior art, a structure of a PWM based power supply adjusting apparatus applicable to a PA in a radio base station is shown in FIG. 1. The power supply adjusting apparatus includes an optional primary converting unit 101, an isolation adjusting and converting unit 102 and a feedback controller, where the input of the optional primary converting unit 101 or the isolation adjusting and converting unit 102 is connected to the input power supply, and the output of the primary converting unit 101 is connected to the isolation adjusting and converting unit 102, and the isolation adjusting and converting unit 102 is also connected to the feedback controller. The output power supply signal of the optional primary converting unit 101 or the isolation adjusting and converting unit 102 is adjusted according to a control signal of the feedback controller so as to obtain a variable output power supply and meet the power requirement of a powered apparatus. The isolation adjusting and converting unit 102 may be implemented by means of any closed-loop control, such as a half-bridge isolation conversion structure, a forward isolation conversion structure or a full-bridge isolation conversion structure. In the structure shown in FIG. 1, the closed-loop adjustment of the input voltage is implemented by controlling in real time the turn-on and turnoff of a switch tube on the primary side of the transformer of the isolation adjusting and converting unit 102. Due to the isolation of the primary side and the secondary side of the transformer, the control signal of the feedback controller requires the help of isolation units (isolation optical coupler and isolation transformer) for transfer.
Specifically, in FIG. 1, a variation in the output voltage Vo is sent to the voltage reference and loop compensation unit 104 on the secondary side of the transformer via the sampling unit 103 and then transferred to the primary side PWM controller integrated circuit (IC) and driving unit 106 via the isolation optical coupler 105. The PWM controller IC and driving unit 106 adjusts the output PWM pulse width in real time according to the variation in Vo so as to control the switch tube and rectifier diodes Q1 to Q8 in the power structure and achieve the purpose of a stable output voltage.
Because of the adoption of isolation feedback control, when the dynamic adjustment range of the output voltage is wide, the adjustment of the output voltage requires the real-time change of the work points of the isolation transformer and optical coupler so that the prior art has at least the following weaknesses:
1. During a process of wide-range and fast real-time voltage adjustment, the PWM needs to control the shutoff of Q3, Q4, Q5 and Q6 in real time, so that the magnetic induction intensity of the isolation transformer is relatively great and likely to exceed the saturated magnetic induction intensity of the isolation transformer. As a result, the isolation transformer is at risk of magnetic saturation and is likely to create audio noise so that the design of a transformer is more difficult.
2. Because of the delay induced by the inherent low-pass feature of such units as the voltage feedback isolation optical coupler, the need for fast dynamic voltage adjustment is even harder to meet by this power supply structure. When the output power changes quickly, due to the bandwidth limitation of the isolation optical coupler and the limitation of the work space of the transformer magnetic core, it is hard for the traditional voltage adjusted power supply to allow the application of high bandwidth signal tracking.